Re: [PATCH, nvptx, 2/2] Reimplement libgomp barriers for nvptx: bar.red instruction support in GCC

[Tom de Vries <tdevries@suse.de>]

On 9/21/22 09:45, Chung-Lin Tang wrote:
> Hi Tom, following the first patch.
> 
> This new barrier implementation I posted in the first patch uses the 
> 'bar.red' instruction. > Usually this could've been easily done with a single line of inline
> assembly. However I quickly
> realized that because the NVPTX GCC port is implemented with all virtual 
> general registers,
> we don't have a register constraint usable to select "predicate registers".
> Since bar.red uses predicate typed values, I can't create it directly 
> using inline asm.
> 
> So it appears that the most simple way of accessing it is with a target 
> builtin.
> The attached patch adds bar.red instructions to the nvptx port, and 
> __builtin_nvptx_bar_red_* builtins
> to use it. The code should support all variations of bar.red (and, or, 
> and popc operations).
> 
> (This support was used to implement the first libgomp barrier patch, so 
> must be approved together)
> 

What I conclude from what you're telling me here is that this is the 
first patch in the series rather than the second.

So, LGTM, please apply it, unless it cannot be applied by itself without 
causing regressions, in which case you need to fix those first.

IWBN if this also included standalone test-cases in 
gcc/testsuite/gcc.target/nvptx, but I suppose we can live without for now.

Thanks,
- Tom

> Thanks,
> Chung-Lin
> 
> 2022-09-21  Chung-Lin Tang  <cltang@codesourcery.com>
> 
> gcc/ChangeLog:
> 
>      * config/nvptx/nvptx.cc (nvptx_print_operand): Add 'p'
>      case, adjust comments.
>      (enum nvptx_builtins): Add NVPTX_BUILTIN_BAR_RED_AND,
>      NVPTX_BUILTIN_BAR_RED_OR, and NVPTX_BUILTIN_BAR_RED_POPC.
>      (nvptx_expand_bar_red): New function.
>      (nvptx_init_builtins):
>      Add DEFs of __builtin_nvptx_bar_red_[and/or/popc].
>      (nvptx_expand_builtin): Use nvptx_expand_bar_red to expand
>      NVPTX_BUILTIN_BAR_RED_[AND/OR/POPC] cases.
> 
>      * config/nvptx/nvptx.md (define_c_enum "unspecv"): Add
>      UNSPECV_BARRED_AND, UNSPECV_BARRED_OR, and UNSPECV_BARRED_POPC.
>      (BARRED): New int iterator.
>      (barred_op,barred_mode,barred_ptxtype): New int attrs.
>      (nvptx_barred_<barred_op>): New define_insn.